How are creatine kinase-MB (CK-MB) isoforms used as cardiac markers?

Updated: Nov 20, 2018
  • Author: Donald Schreiber, MD, CM; Chief Editor: Barry E Brenner, MD, PhD, FACEP  more...
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Answer

Answer

The CK-MB isoenzyme exists as 2 isoforms: CK-MB1 and CK-MB2. Laboratory determination of CK-MB actually represents the simple sum of the isoforms CK-MB1 and CK-MB2. CK-MB2 is the tissue form and initially is released from the myocardium after MI. It is converted peripherally in serum to the CK-MB1 isoform rapidly after symptom onset.

Normally, the tissue CK-MB1 isoform predominates; thus, the CK-MB2/CK-MB1 ratio is typically less than 1. A result is positive if the CK-MB2 is elevated and the ratio is greater than 1.7.

CK-MB2 can be detected in serum within 2-4 hours after onset and peaks at 6-9 hours, making it an early marker for acute MI. Two large studies evaluating its use revealed a sensitivity of 92% at 6 hours after symptom onset, compared with 66% for CK-MB and 79% for myoglobin. [36, 37] The major disadvantage of this assay is that it is relatively labor intensive for the laboratory.


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